Image recording method and image recording apparatus

ABSTRACT

An image recording method comprises the steps of: acquiring first recording characteristic information of recording elements of a recording head by reading a first test pattern formed with ejecting ink droplet from the recording elements; obtaining first density unevenness correction information based on the first recording characteristic information; acquiring second recording characteristic information of the recording element by reading a second test pattern different from the first test pattern formed with ejecting ink droplet from the recording elements; obtaining second density unevenness correction information based on the second recording characteristic information; correcting image data based on the first and second density unevenness correction information to calculate density unevenness-corrected image data; and calculating an ejection pattern of the recording element based on the unevenness-corrected image data.

The entire contents of all documents cited in this specification areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an image recording method and an imagerecording apparatus, each for recording an image on a recording mediumby ejecting ink droplets from an inkjet head.

As a method of recording an image on a recording medium, there isprovided an inkjet recording method in which ink droplets are ejectedfrom an inkjet head to form an image.

The inkjet recording method has a problem in that, because ink dropletsare ejected from a plurality of ejection ports, variation in ejectioncharacteristic of each recording element provided with the ejection portcauses density unevenness in a recorded image. This problem isparticularly conspicuous in a case of a single-pass type inkjet methodin which, with a line-type inkjet head being fixed, a recording mediumis conveyed once in one direction, whereby an image is recorded on theentire surface of the recording medium.

As a method of correcting the density unevenness, there are provided amethod in which the density unevenness is corrected by changing, foreach recording element, an ejection driving condition in accordance withthe density unevenness and adjusting the dot diameter or the dotdensity, and a method which eliminates the influence of the densityunevenness on a recorded image by correcting image data in accordancewith the density unevenness.

The correction method by changing the ejection driving condition is sucha method that makes a change with respect to the ink droplets to beejected from an inkjet head, and hence, at the time of implementation,there exists a limitation on the driving method of the inkjet head andthe correction range. On the other hand, the method by correcting theimage data in accordance with the density unevenness can be implementedby correcting data without changing the actual ink droplets to beejected from the inkjet head, that is, without changing the inkjet headitself (that is, without physical change thereof). Therefore, thismethod has greater flexibility, and various types of such correctionmethods have been proposed.

Here, in the case of converting image data, γ conversion is performedfor each recording element with the use of a 1D-LUT.

As a method for obtaining a correction curve (unevenness correctioncoefficient) of the 1D-LUT, there are proposed a method in which, as inJP 04-18356 A, the density of an area corresponding to the position of arecording element is measured to thereby correct the density unevennessof a print area, and a method in which, as in JP 2006-264069 A and JP2006-347164 A, the accuracy of the position of a droplet ejected from arecording element is measured with high precision, and a correctioncoefficient is calculated based on the positional information.

Here, JP 04-18356 A describes a method in which ink droplets are ejectedfrom all the recording elements to create, on a recording medium, asolid image having a given density (for example, density of 50%), and,based on density variation of the image, the density unevenness iscalculated and then corrected. Further, JP 04-18356 A also describescreating, by calculating only the amount of change from the last densityunevenness correction data, correction data in a shorter period of timecompared to creating correction data again from the beginning.

Further, JP 2006-264069 A gives a description as follows. Ink dropletsare ejected from each ejection nozzle to form a test pattern, in whichlines are made by the respective ejection nozzles. After the testpattern is read, based on a density profile of each line included in theread test pattern, a landing position error of the ink droplets ejectedfrom each nozzle is detected, and, based on the landing position error,the density unevenness is corrected. Further, in JP 2006-264069 A, thereis a description that, at the time of detection of the landing positionerror, the error characteristic of an ejection amount from a nozzle maybe detected.

Further, in JP 2006-347164 A, there is a description that, based on thedetected landing position of an ink droplet, a correction coefficient iscalculated.

Here, to attain high-precision print quality, a pixel density of, forexample, 1,200 dpi or higher is required as the pixel density of theinkjet head. Accordingly, one droplet (impact point) becomes smaller,and hence an interval error between the impact points becomes extremelysmall as well.

Further, the method of measuring the image density of an areacorresponding to the droplet landing position of each recording element,which is described in JP 04-18356 A, requires a resolution at leasttwice as high as the resolution of the image so that the correspondencebetween the position of the recording element and the measurement in therelevant area can be obtained with high precision.

Accordingly, in a case where the method described in JP 04-18356 A isused for correcting density unevenness of a high-pixel-density image asdescribed above, a resolution of 2,400 dpi or higher is required. As aresult, it takes an extremely long period of time to perform scanning,measurement data transfer, and measurement data processing.

Incidentally, with regard to the method in which the area density ismeasured, it is known that even such a method, in which reading duringthe measurement is performed in a low resolution so as to reduce therequired period of time, and then the density of each recording elementarea is estimated, has the effect of correcting unevenness. However, ifa scanning resolution is made lower, the effect of unevenness correctionbecomes insufficient for unevenness having high-frequency componentshigher than the scanning resolution.

In addition, the method described in JP 04-18356 A has a problem in thatsufficient precision cannot be attained by performing the unevennesscorrection once.

Further, when used for the density unevenness correction of a high-pixeldensity image as described above, the methods described in JP2006-264069 A and JP 2006-347164 A, too, require a resolution of 2,400dpi or higher in order to measure a dot position with high precision,and have a problem in that it takes an extremely long period of time toperform the scanning, the measurement data transfer, and the measurementdata processing.

Particularly, a method in which a dot position and a dot diameter aredetected based on the density profile as in the method described in JP2006-264069 A requires particularly high-precision measurement due tothe need to calculate the outer shape and density of a dot accurately.Besides, there is a problem in that, because the calculation isperformed for each recording element, the calculation amount becomeslarger, and it takes a longer period of time for the data processing.

Further, with this method, another problem is that, in some cases,low-frequency unevenness is not sufficiently eliminated depending on thetype of position error.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an image recordingmethod and an image recording apparatus which are capable of, by solvingthe problems inherent in the above-mentioned prior art, detectingdensity unevenness efficiently in an appropriate manner, carrying outcorrection processing based on the detected density unevenness, andrecording an image in which the density unevenness has been corrected.

An image recording method according to the present invention comprises:a first recording characteristic information acquiring step of causingeach of recording elements of a recording head to eject ink droplet,forming a first test pattern on a recording medium, reading the formedfirst test pattern, and acquiring first recording characteristicinformation of the recording element based on a result of the reading; afirst density unevenness correction information calculating step ofobtaining first density unevenness correction information based on thefirst recording characteristic information; a second recordingcharacteristic information acquiring step of causing the each of therecording elements of the recording head to eject the ink droplet,forming a second test pattern different from the first test pattern onthe recording medium, reading the second test pattern, and acquiringsecond recording characteristic information of the recording elementbased on a result of the reading; a second density unevenness correctioninformation calculating step of obtaining second density unevennesscorrection information based on the second recording characteristicinformation; a third density unevenness correction informationcalculating step of obtaining third density unevenness correctioninformation based on the first density unevenness correction informationand the second density unevenness correction information; a densitycorrection processing step of correcting image data based on the thirddensity unevenness correction information to calculate densityunevenness-corrected image data; and an ejection control signalcalculating step of calculating an ejection pattern of the recordingelement based on the unevenness-corrected image data.

An image recording apparatus according to the present inventioncomprises: a recording head comprising a plurality of recording elementsfor ejecting an ink droplet toward a recording medium; movement meansthat causes the recording head and the recording medium to move relativeto each other; recording operation control means that records an imageon the recording medium by causing the recording head to eject the inkdroplet toward the recording medium while the recording head and therecording medium are moved relative to each other; first test patternreading means that reads a first test pattern formed on the recordingmedium by ejecting the ink droplet from each of the plurality ofrecording elements of the recording head; first recording characteristicinformation acquiring means that acquires first recording characteristicinformation of the each of the plurality of recording elements based ona result of the reading of the first test pattern; first densityunevenness correction information calculating means that obtains firstdensity unevenness correction information based on the first recordingcharacteristic information; second test pattern reading means that readsa second test pattern different from the first test pattern, which isformed on the recording medium by ejecting the ink droplet from the eachof the plurality of recording elements of the recording head; secondrecording characteristic information acquiring means that acquiressecond recording characteristic information of the each of the pluralityof recording elements based on a result of the reading of the secondtest pattern; second density unevenness correction informationcalculating means that obtains second density unevenness correctioninformation based on the second recording characteristic information;third density unevenness correction information calculating means thatobtains third density unevenness correction information based on thefirst density unevenness correction information and the second densityunevenness correction information; density correction processing meansthat corrects image data based on the third density unevennesscorrection information to calculate density unevenness-corrected imagedata; and ejection pattern calculating means that calculates an ejectionpattern of the each of the plurality of recording elements based on theunevenness-corrected image data.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a front view illustrating a schematic configuration of animage recording apparatus;

FIG. 2 is a top view illustrating a conveying attraction belt and arecording head unit of the image recording apparatus illustrated in FIG.1;

FIG. 3A is a front view illustrating an arrangement pattern of ejectionportions of a recording head;

FIG. 3B is an enlarged cross-section illustrating one ejection portionof the recording head illustrated in FIG. 3A;

FIG. 4 is a schematic diagram illustrating a configuration of an inksupply system and the surroundings of a head in the image recordingapparatus;

FIG. 5 is a block diagram illustrating a system configuration of acontrol portion illustrated in FIG. 1;

FIG. 6 is a block diagram illustrating a system configuration of a printcontrol section illustrated in FIG. 5;

FIG. 7A is a side view illustrating a relation between each ejectionportion of a recording head and a landing position of an ink droplet;

FIG. 7B is a top view associated with the side view of FIG. 7A;

FIG. 8 is a flow chart illustrating steps of a process for creatingthird density unevenness correction information;

FIG. 9A is a schematic diagram illustrating an example of a first testpattern;

FIG. 9B is a partially enlarged view of FIG. 9A;

FIG. 10 is a schematic diagram illustrating an example of a second testpattern;

FIG. 11A is a graph illustrating an example of first density unevennesscorrection information for one recording element;

FIG. 11B is a graph illustrating an example of second density unevennesscorrection information for one recording element;

FIG. 11C is a graph illustrating an example of the third densityunevenness correction information for one recording element;

FIG. 12 is a flow chart illustrating a process for processing image dataused for printing; and

FIG. 13 is a front view illustrating another example of the arrangementpattern of the ejection portions of a recording head.

DETAILED DESCRIPTION OF THE INVENTION

An image recording method and an image recording apparatus according tothe present invention are described in detail with reference to anembodiment thereof as illustrated in the accompanying drawings.

FIG. 1 is a front view illustrating a schematic configuration of animage recording apparatus 10 as an embodiment of the image recordingapparatus of the present invention, which employs the image recordingmethod of the present invention. FIG. 2 is a top view illustrating anattraction belt conveying portion 36 and a recording head unit 50 of theimage recording apparatus 10 illustrated in FIG. 1.

The image recording apparatus 10 fundamentally includes a feedingportion 12 for feeding a recording medium P, a conveying portion 14 forconveying the recording medium P fed by the feeding portion 12 in amanner to keep its flatness, a drawing portion 16 which is placedopposite to the conveying portion 14 and includes a recording head unit50 for drawing an image on the recording medium P and an inkstorage/filling portion 52 for storing ink to be fed to the recordinghead unit 50, a heat-pressing portion 18 for heating and pressing therecording medium P on which the image has been drawn, a dischargingportion 20 for discharging to the outside the recording medium P onwhich the image has been drawn, a scanner 24 for reading the imagerecorded on the recording medium P by the drawing portion 16, and acontrol portion 22 for controlling those components.

The feeding portion 12 includes a magazine 30, a heating drum 32, and acutter 34.

The magazine 30 stores the recording medium P in a rolled form. At thetime of image drawing, the recording medium P is fed to the heating drum32 from the magazine 30.

The heating drum 32 is placed downstream of the magazine 30 along theconveying path of the recording medium P, and heats the recording mediumP delivered from the magazine 30 in a state in which the recordingmedium P is bent in a direction opposite to the direction in which therecording medium P is bent during the storage in the magazine 30.

Through heating by the heating drum 32, the recording medium P, whichhas become curled while stored in the magazine 30, is straightened. Inother words, the heating drum 32 performs decurling processing for therecording medium P.

At this point, desirably, the heating temperature is so controlled thatthe recording medium P is slightly curled toward the printed sidethereof.

The cutter 34 includes a fixed blade 34A having a length larger than thewidth of the conveying path of the recording medium P and a round blade34B which moves along the fixed blade 34A. The fixed blade 34A is placedon the side of the conveying path, on which an image is to be drawn onthe surface of the recording medium P, and the round blade 34B is placedon the opposite side of the conveying path.

The cutter 34 cuts the recording medium P fed through the heating drum32 into a desired size.

Here, in this embodiment, the feeding portion 12 is provided with onemagazine, but the present invention is not limited thereto. For example,a plurality of magazines storing various recording media different inpaper width, paper quality, or type may be provided. Moreover, insteadof the magazine, or in addition to the magazine, it is possible toemploy a cassette containing a stack of cut sheets provided by cutting aweb of recording medium into a predetermined length. In a case whereonly the recording medium previously cut into sheets of a predeterminedlength is used as the recording medium P, the above-mentioned heatingroller and cutter do not necessarily have to be provided.

Further, in a case of a configuration in which a plurality of types ofrecording sheets are made available for use by employing a plurality ofmagazines and/or cassettes, it is desirable that ink ejection control beperformed in the following manner. An information-recorded member suchas a bar code or a wireless tag, on which information on paper type isrecorded, is attached to each of the magazines and/or cassettes, and, byreading the information of the information-recorded member by a givenreading device, the type of a sheet to be used is automaticallydetermined to realize appropriate ink ejection in accordance with thetype of the sheet.

The conveying portion 14 includes the attraction belt conveying portion36, an attraction chamber 39, a fan 40, a belt cleaning portion 42, anda heating fan 44. The conveying portion 14 conveys the recording mediumP, which has been subjected to the decurling processing and cut into apredetermined length in the feeding portion 12, to a drawing position,that is, a position at which an image is drawn by the drawing portion 16described below.

The attraction belt conveying portion 36 is placed downstream of thecutter 34 along the conveying path of the recording medium P, andincludes a roller 37 a, a roller 37 b, and a belt 38.

The belt 38 is an endless belt having a width larger than the width ofthe recording medium P, and is extended between the roller 37 a and theroller 37 b under tension. Further, the belt 38 has numerous suctionholes (not shown) formed in the plane body thereof.

Further, the attraction belt conveying portion 36 is kept flat at leastat an image drawing (printing) position, that is, in its part opposed toa nozzle surface of the recording head unit 50 (described below) of thedrawing portion 16, and at an image detection position, that is, in itspart opposed to a sensor surface of the scanner (described below),relative to the nozzle surface and the sensor surface.

At least one of the roller 37 a and the roller 37 b, on which the belt38 is mounted, is connected to a motor (not shown), and the power of themotor is transmitted to the belt 38 via at least one of the roller 37 aand the roller 37 b. As a result, the belt 38 is driven in a clockwisedirection in FIG. 1, whereby the recording medium P held on the belt 38is conveyed from the left to the right in FIG. 1.

Here, conveying means for the recording medium P is not limited inparticular, and, instead of the attraction belt conveying portion 36, aroller nip conveyance mechanism can be employed. However, in the case ofthe roller nip conveyance employed in a drawing area, there is a problemin that the image easily becomes smeared because the printed surface ofa sheet and the roller come into contact immediately after printing.Hence, in a printing area, such attraction belt conveyance as in thisembodiment is desirable because nothing comes into contact with an imagesurface.

The attraction chamber 39 is provided on the inner side of the belt 38at a position opposed to the nozzle surface of the recording head unit50 (described below) of the drawing portion 16 and the sensor surface ofthe scanner 24. Further, the fan 40 is connected to the attractionchamber 39. A negative pressure is created in the attraction chamber 39by the suction through the fan 40, whereby the recording medium P on thebelt 38 is held on the belt 38 in an attracted manner.

By attracting the recording medium P to the belt 38, the recordingmedium P can be stably held.

The belt cleaning portion 42 is placed on the outer side of the belt 38,that is, opposite to the outer circumferential surface of thering-shaped belt, and is spaced apart from the conveying path of therecording medium P. Specifically, the belt 38 passes through the drawingportion 16, and after discharging the recording medium P to a pressureroller pair 54 described below, passes through a position opposed to thebelt cleaning portion 42.

The belt cleaning portion 42 removes ink which has been attached on thebelt 38 due to borderless printing or the like. For the belt cleaningportion 42, for example, a method of performing nipping with a brushroll, a water absorption roll, or the like, an air-blow method in whichcleaning air is blown against the belt, or a combination thereof may beemployed. In the case of nipping with a cleaning roll, a larger cleaningeffect can be attained by making the belt linear speed and the rollerlinear speed different from each other.

The heating fan 44 is placed on the outer side of the belt 38, andupstream of the recording head unit 50 (described below) of the drawingportion 16 along the conveying path of the recording medium P.

The heating fan 44 blows heated air onto the recording medium P beforedrawing to heat the recording medium P. If the recording medium P isheated immediately before drawing, the ink becomes easy to dry afterlanding.

The drawing portion 16 includes the recording head unit 50 for drawing(printing) an image, and the ink storage/filling portion 52 forsupplying ink to the recording head unit 50.

The recording head unit 50 includes recording heads 50K, 50C, 50M, and50Y, and is placed opposite to the surface of the belt 38, on which therecording medium P is placed.

The recording heads 50K, 50C, 50M, and 50Y are piezo-electric inkjetheads which eject black (K) ink, cyan (C) ink, magenta (M) ink, andyellow (Y) ink from ejection portions, respectively. The recording heads50K, 50C, 50M, and 50Y, each opposed to the surface of the belt 38, onwhich the recording medium P is placed, are arranged downstream of theheating fan 44 in the conveying direction of the recording medium P inthis order, with the head 50K being nearest the fan 44. Further, therecording heads 50K, 50C, 50M, and 50Y are connected to the inkstorage/filling portion 52 and the control portion 22.

Further, as illustrated in FIG. 2, the recording heads 50K, 50C, 50M,and 50Y are each a full-line inkjet head in which a plurality ofejection portions (nozzles) are arranged in line over such a regionwhose width in a direction orthogonal to the conveying direction of therecording medium P exceeds the maximum width of the recording medium Pto be conveyed. Here, the configuration of the inkjet head is describedbelow in detail along with a relation thereof with the inkstorage/filling portion 52.

With the full-line recording heads as in this embodiment, an image canbe recorded on the entire surface of the recording medium P by movingonce the recording medium P and the drawing portion 16 relative to eachother (in other words, by one scan) in a direction orthogonal to thedirections of ejection portion arrangement of the recording heads(auxiliary scanning direction). With this configuration, compared to theshuttle recording head in which a recording head runs back and forth inthe main scanning direction, it is possible to perform high speedprinting, which therefore leads to an improved productivity.

The ink storage/filling portion 52 includes ink supply tanks for storingcolor inks which correspond to the recording heads 50K, 50C, 50M, and50Y, respectively.

For the ink supply tank, for example, a system in which the tank isreplenished with ink from a replenishing inlet (not shown) when theremaining ink is scarce, or a cartridge system in which an almost emptytank is replaced with a new one can be employed.

The ink supply tanks of the ink storage/filling portion 52 arecommunicating with the recording heads 50K, 50C, 50M, and 50Y via tubes(not shown), respectively, so as to supply ink to the recording heads50K, 50C, 50M, and 50Y.

Here, it is desirable that the ink storage/filling portion 52 beprovided with notification means (display means, warning tone generationmeans, etc.) for making, when the remaining ink becomes scarce, anotification to that effect, and include a mechanism for preventingerroneous filling among colors.

Further, in a case where ink types are changed in accordance with theintended use, it is desirable that the cartridge system be used. Inaddition, it is desirable that, by identifying information on the inktype through a bar code or the like, such ejection control thatcorresponds to the ink type be performed.

Next, the configurations of the recording heads 50K, 50C, 50M, and 50Yare described. Here, the recording heads 50K, 50C, 50M, and 50Y have thesame configuration except for the colors of ink to be ejected, and hencethe recording head 50K is described as an example hereinbelow.

FIG. 3A is a front view illustrating an arrangement pattern of theejection portions 60 of the recording head 50K, while FIG. 3B is anenlarged cross-section illustrating one ejection portion 60 of therecording head 50K.

As illustrated in FIG. 3A, the recording head 50K includes a pluralityof recording elements (hereinbelow, referred to as “ejection portions”)60 which eject ink droplets. The ejection portions 60 are arranged inline at fixed intervals.

As illustrated in FIG. 3B, one ejection portion 60 includes an inkchamber unit 61 and an actuator 66. Further, the ink chamber unit 61 isconnected to a common flow path 65. The common flow path 65 is connectedto the ink chamber units 61 of all the ejection portions 60.

The ink chamber unit 61 includes a nozzle 62, a pressure chamber 63, anda supply opening 64.

The nozzle 62, which is an opening portion for ejecting ink droplets,has one end opened on a surface opposed to the recording medium P andthe other end connected to the pressure chamber 63.

The pressure chamber 63 has a rectangular shape in which the planarshape of the faces perpendicular to the ejecting direction of inkdroplets is substantially square, and two corner portions on a diagonalline are connected to the nozzle 62 and the supply opening 64,respectively.

The supply opening 64 has one end connected to the pressure chamber 63,and the other end communicating with the common flow path 65.

The actuator 66 is placed on the side (upper side) of the pressurechamber 63 opposite to the side on which the pressure chamber 63 isconnected to the nozzle 62 and the supply opening 64, and includes apressure plate 67 and a separate electrode 68.

In the actuator 66, a driving voltage is applied to the separateelectrode 68 to thereby deform the pressure plate 67.

An ink ejection method of the ejection portion 60 is described.

Ink is supplied to the pressure chamber 63 and the nozzle 62 from thecommon flow path 65 via the supply opening 64.

In a state in which the pressure chamber 63 and the nozzle 62 are filledwith ink, when a driving voltage is applied to the separate electrode68, the pressure plate 67 is deformed to pressurize the pressure chamber63, whereby the ink is ejected from the nozzle 62. By thus driving theactuator 66, ink droplets can be ejected from the nozzle 62.

Further, after the ink is ejected, new ink is supplied to the pressurechamber 63 from the common flow path 65 through the supply opening 64.

It should be noted that the structural arrangement of the ejectionportion of the present invention is not limited to the illustratedexample. Further, in this embodiment, there is adopted a method in whichan ink droplet is ejected by deformation of the actuator 66 as typifiedby a piezo-electric element. However, the present invention is notlimited thereto with regard to a method of ejecting ink, and, instead ofa piezo-electric method, various kinds of methods may be employed,including a thermal inkjet method in which a heating element such as aheater heats ink to generate bubbles, and an ink droplet is ejected bythe pressure of the bubbles.

Next, a relation between the recording head unit 50 and the inkstorage/filling portion 52 is described in more detail.

FIG. 4 is a schematic diagram illustrating a configuration of the inksupply system and the surroundings of the heads of the image recordingapparatus 10. It should be noted that relations between the respectiverecording heads 50K, 50C, 50M, and 50Y and the ink storage/fillingportion 52 are the same except for the type of ink. Hence, only therelation between the recording head 50K and the ink storage/fillingportion 52 is described, and description on the relations between therespective recording heads 50C, 50M, and 50Y and the ink storage/fillingportion 52 is omitted.

An ink supply tank 70 is a tank for storing ink having a color whichcorresponds to the recording head 50K, that is, black ink, and is placedinside the ink storage/filling portion 52. Further, the recording head50K and the ink supply tank 70 are coupled to each other via a supplypipe.

In the middle of the flow path connecting the ink supply tank 70 and therecording head 50K, a filter 72 for removing foreign material andbubbles is provided. It is desirable that the filter mesh size of thefilter 72 be equal to or smaller than a nozzle diameter (in general,approximately 20 μm).

It is desirable that a sub-tank be provided in the vicinity of therecording head 50K or be incorporated in the recording head 50K. Withthe sub-tank being provided, it is possible to obtain a damper effect,which prevents fluctuations in the internal pressure of the head, andhence refilling can be improved.

Further, as illustrated in FIG. 4, the image recording apparatus 10 isprovided, as means for preventing the nozzle 62 from drying orpreventing the ink viscosity in the vicinity of the nozzle 62 fromincreasing, with a cap 74, a suction pump 77, and a collection tank 78,and is also provided with a cleaning blade 76 as means for cleaning anozzle surface of the recording head 50K, that is, a surface at whichthe nozzle 62 is opened.

A maintenance unit including the cap 74 and the cleaning blade 76 iscapable of moving relative to the recording head 50K with the aid of amovement mechanism (not shown), and is moved, as needed, from a givenpull-off position to a maintenance position below the recording head50K.

At the maintenance position, the cap 74 is placed opposite to therecording head 50K, and supported in a vertically-movable mannerrelative to the recording head unit 50 with the aid of a liftingmechanism (not shown).

The cap 74 is lifted up to a given position by the lifting mechanism(not shown) under conditions of power-off or print standby, and isbrought into close contact with the recording head 50K, whereby thenozzle surface of the recording head 50K is covered with the cap 74.

In this manner, by covering the nozzle surface of the recording head 50Kwith the cap 74 to make a sealed state, it is possible to prevent theink inside the nozzle from drying and becoming stiff, and prevent theink viscosity from increasing due to evaporation of ink solvent.

Alternatively, at the time of maintenance or at fixed intervals, the inkmay be ejected from the nozzle 62 by driving the actuator 66 after thecap 74 is mounted on the recording head 50K.

If, during the drawing or on standby, a particular nozzle 62 of therecording head 50K is used less frequently, and the situation in whichthe ink is not ejected is continued for a certain period of time orlonger, the ink solvent in the vicinity of that nozzle evaporates,making the ink viscosity higher. Then, in some cases, it becomesimpossible to eject the ink from the nozzle 62. However, bypreliminarily ejecting the ink to the cap 74 (purging, dummy ejection,or spitting), it is possible to discharge deteriorated ink inside thenozzle 62 (ink in the vicinity of the nozzle, which has an increasedviscosity) from the nozzle 62. With this configuration, it becomespossible to prevent the ink from clogging in the nozzle 62, and also,variations in ejection characteristic among the nozzles 62, which resultfrom different ink viscosities, can be prevented. Therefore, inkdroplets can be ejected stably.

The suction pump 77 has one end connected to the cap 74 and the otherend connected to the collection tank 78. In a state in which the cap 74is mounted on the recording head 50K in close contact with each other,the suction pump 77 performs suction, whereby the ink inside the nozzle62 is sucked out. Further, the ink sucked out by the suction pump 77 isdelivered to the collection tank 78.

In this manner, by sucking out the ink by the suction pump 77, even ifthe ink inside the recording head 50K (inside the pressure chamber 63)has bubbles mixed therein and cannot be ejected from the nozzle byoperating the actuator 66, for example, the ink inside the pressurechamber 63 (ink with bubbles mixed therein) is sucked out by the suctionpump 77, and thereby can be removed by the suction. In other words, itis possible to create a situation in which ink droplets can be ejected.

It should be noted that the suction by the suction pump 77 is desirablyalso performed when ink is initially loaded into the head, or when thehead is used again after suspension over a long period of time, so as tosuck out deteriorated ink having an increased viscosity (which hasbecome solidified).

Incidentally, the suction by the suction pump 77 is performed withrespect to the entire ink inside the pressure chamber 63, whichtherefore makes the amount of consumed-ink large. Accordingly, when thedegree of increase of the ink viscosity is small, the above-mentionedmode in which ejection of ink droplets to the cap 74 (preliminaryejection) is performed is more desirable.

The cleaning blade 76 is formed with an elastic material such as rubber,and is placed, at the time of maintenance, in contact with the nozzlesurface of the recording head 50K. Further, the cleaning blade 76 isconnected to a blade-moving mechanism (wiper) (not shown), and is slidon the nozzle surface by the blade-moving mechanism. With the cleaningblade 76 sliding on the nozzle surface, ink droplets and foreignmaterial attached to the nozzle surface are wiped out and removed. Inother words, the nozzle surface can be cleaned up.

It should be noted that, when adherents on the ink ejection surface arecleaned up by the blade mechanism, the preliminary ejection is desirablyperformed so as to prevent foreign material from being intruded into thenozzle 62 by the cleaning blade 76.

Referring back to FIG. 1, the other portions of the image recordingapparatus 10 are described.

The heat-pressing portion 18, which includes a post-drying portion 53and a pressure roller pair 54, heats and presses the recording medium Pon which an image has been drawn in the drawing portion 16, whereby theimage area is dried and fixed.

The post-drying portion 53 is placed at a position downstream of therecording head unit 50 along the conveying path of the recording mediumP and opposed to the belt 38. The post-drying portion 53 is, forexample, a heating fan, and blows heated air onto the image surface ofthe recording medium P to dry the drawn image.

Here, it is desirable that a heating fan be used for the post-dryingportion 53 to blow heated air.

With the aid of the heating fan drying the ink of the image area on therecording medium P, it is possible to dry the image area with no contacttherewith. With this configuration, it is possible to prevent an imagedefect or an image smudge from occurring to the image drawn on therecording medium P.

Further, the pressure roller pair 54 is placed downstream of thepost-drying portion 53 along the conveying path of the recording mediumP. The pressure roller pair 54 conveys in a sandwiching manner therecording medium P, which has been separated from the belt 38 afterpassing through the post-drying portion 53.

The pressure roller pair 54, which is means for controlling the glosslevel of the surface of an image, applies a pressure with its pressurerollers having a given surface asperity to the image surface of therecording medium P conveyed by the attraction belt conveying portion 36while heating the image surface, thereby transferring the asperity ontothe image surface.

Further, in a case where porous paper is printed using dye-based ink orin another case, by closing pores of the paper through pressing, it ispossible to prevent contact with a substance which causes dyestuffmolecules to be broken, such as ozone. As a result, the weatherabilityof the image can be enhanced.

Further, the image recording apparatus 10 has a cutter (second cutter)56 placed downstream of the heat-pressing portion 18 along the conveyingpath of the recording medium P.

The cutter 56 includes a fixed blade 56A and a round blade 56B, and, ina case where a normal image and an image for detecting displacement areformed on the recording medium P, separates the normal image portionfrom the image portion for detecting displacement.

The discharging portion 20, which includes a first discharging portion58A and a second discharging portion 58B, is placed downstream of thecutter 56 in the conveying direction of the recording medium P. Thedischarging portion 20 discharges the recording medium P on which theimage has been fixed by the heat-pressing portion 18.

Here, in this embodiment, in accordance with the image recorded on therecording medium P, selection means (not shown) switches over betweenthe discharging portions for discharging the recording medium P. Arecording medium on which a normal image has been drawn is delivered tothe first discharging portion 58A, while a recording medium on which animage for detecting displacement has been drawn or an unnecessaryrecording medium is delivered to the second discharging portion 58B.

Incidentally, it is desirable that the discharging portion 20 beprovided with a sorter which collects images on an order basis.

It should be noted that, as in this embodiment, two discharging portionsare desirably provided to enable selection between the dischargingportions depending on the purpose, but the present invention is notlimited thereto. Only one discharging portion may be provided, anddischarge all recording media. Alternatively, three or more dischargingportions may be provided.

Next, the control portion 22 controls the conveyance, heating, drawing,image unevenness detection, and the like for the recording medium P,which are performed by the feeding portion 12, the conveying portion 14,the drawing portion 16, the heat-pressing portion 18, the dischargingportion 20, and the scanner 24. The configuration of the control portion22 is described below in detail.

The scanner 24 is opposed to the outer surface (outer circumferentialsurface) of the belt 38, and is placed at a position between therecording head unit 50 and the post-drying portion 53. The scanner 24includes an image sensor (line sensor or the like) for imaging (i.e.,reading) a test pattern formed by the drawing portion 16, and reads animage recorded on a recording medium with the image sensor. It should benoted that the scanner 24 is capable of reading an image with at leasttwo different resolutions, and switches the resolution for reading inaccordance with the mode.

The scanner 24 according to this embodiment is configured by a linesensor having a line of light receiving elements, which ranges beyondthe width for ink ejection performed by each recording head 50K, 50C,50M, or 50Y (image recording width). This line sensor is a colorseparation line CCD sensor having a red (R) sensor line in whichphotoelectric conversion elements (pixels) provided with red filters arearranged in line, a green (G) sensor line provided with green filters,and a blue (B) sensor line provided with a blue filters. It should benoted that, instead of the line sensor, an area sensor in which lightreceiving elements are two-dimensionally arranged can be employed.

FIG. 5 is a block diagram illustrating a system configuration of thecontrol portion 22 of the image recording apparatus 10.

The control portion 22 includes a communication interface 102, a systemcontroller 104, an image memory 106, a motor driver 108, a heater driver110, a print control section 112, an image buffer memory 114, and a headdriver 116. As described above, the control portion 22 controls theconveyance, heating, drawing, detection of displacement, and the likefor the recording medium P, which are performed by the feeding portion12, the conveying portion 14, the drawing portion 16, the heat-pressingportion 18, the discharging portion 20, and the scanner 24.

The system controller 104 is a control section for controlling suchsections as the communication interface 102, the image memory 106, themotor driver 108, and the heater driver 110. The system controller 104is configured by a central processing unit (CPU) and peripheral circuitsthereof, and controls communication with a host computer 118 and readingfrom/writing to the image memory 106, as well as generates controlsignals for controlling a motor 98 for the conveyance system and aheater 99.

The communication interface 102 receives image data transmitted from thehost computer 118, and then transmits the image data to the systemcontroller 104. As the communication interface 102, serial interfaces,such as a USB, the IEEE 1394, the Ethernet (registered trademark), and awireless network, and parallel interfaces such as centronics can beused. Further, a buffer memory may be provided to make a communicationspeed higher.

The image memory 106 is storage means for temporarily storing an imagewhich has been input via the communication interface 102, and data isread therefrom/written thereto via the system controller 104. The imagememory 106 is not limited to a memory comprised of semiconductordevices, and such a magnetic medium as a hard disk may be used.

The image data transmitted from the host computer 118 is loaded into theimage recording apparatus 10 via the communication interface 102, andthen is stored in the image memory 106 via the system controller 104.

The motor driver 108 is a driver (drive circuit) for driving the motor98 in accordance with an instruction from the system controller 104.

The heater driver 110 is a driver for driving the heater 99 of thepost-drying portion 53 or the like, in accordance with an instructionfrom the system controller 104.

The print control section 112 is a control section which has a signalprocessing function, that is to say, performs, under the control of thesystem controller 104, such processing as various kinds of processes forgenerating a print control signal from the image data within the imagememory 106, and density unevenness correction, and supplies to the headdriver 116 the print control signal (print data) generated from theimage data.

The print control section 112 carries out required signal processing,and controls, based on the image data, ejection timing of ink dropletsof the recording head unit 50 via the head driver 116. In this manner,desired dot placement can be realized.

Here, FIG. 6 is a block diagram illustrating a system configuration ofthe print control section 112.

As illustrated in FIG. 6, the print control section 112 includes animage data transfer section 120, a density correction processing section122, a first density unevenness correction information calculatingsection 124, a second density unevenness correction informationcalculating section 126, a third density unevenness correctioninformation calculating section 128, and a binarization processingsection 130. Further, the print control section 112 is provided with theimage buffer memory 114.

The image buffer memory 114 temporarily stores such data as image dataand parameters at the time of the image data processing performed by theprint control section 112. It should be noted that, in FIGS. 5 and 6,the image buffer memory 114 is illustrated as being attached to theprint control section 112, but the image memory 106 can also be used asthe image buffer memory 114 at a time. Further, it is also possible tointegrate the print control section 112 with the system controller 104into a system configured by one processor.

The image data transfer section 120 receives image data supplied (input)from the system controller 104, and transmits the image data to thedensity correction processing section 122 or the binarization processingsection 130. In accordance with the type of the supplied image data, theimage data transfer section 120 switches over between the densitycorrection processing section 122 and the binarization processingsection 130 as to where the image data is to be transmitted.

Here, if necessary, the image data may be temporarily stored in theimage buffer memory 114. Then, the image data is retrieved from theimage buffer memory 114 and transmitted to the density correctionprocessing section 122 or the binarization processing section 130.

The density correction processing section 122 carries out densityunevenness correction processing with respect to the image data whichhas been transferred from the image data transfer section 120, based ondensity unevenness correction information (described below) suppliedfrom the second density unevenness correction information calculatingsection 126 or the third density unevenness correction informationcalculating section 128, and then transmits unevenness-corrected imagedata to the binarization processing section 130.

Based on a first test pattern which is read by the scanner 24, the firstdensity unevenness correction information calculating section 124calculates, as first density unevenness correction information,high-frequency density unevenness caused by a landing position error ofthe ejection portions. Further, the first density unevenness correctioninformation calculating section 124 transmits the calculated firstdensity unevenness correction information to the third densityunevenness correction information calculating section 128. In addition,if necessary, the first density unevenness correction informationcalculating section 124 transmits the first density unevennesscorrection information to the density correction processing section 122.

Based on a second test pattern which is read by the scanner 24, thesecond density unevenness correction information calculating section 126calculates, as second density unevenness correction information,low-frequency density unevenness caused by a fluctuation of thediameters of droplets (or landing diameters of droplets) ejected fromthe ejection portions. The second density unevenness correctioninformation calculating section 126 transmits the calculated seconddensity unevenness correction information to the third densityunevenness correction information calculating section 128.

The third density unevenness correction information calculating section128 calculates third density unevenness correction information based onthe first density unevenness correction information transmitted from thefirst density unevenness correction information calculating section 124and the second density unevenness correction information transmittedfrom the second density unevenness correction information calculatingsection 126. The third density unevenness correction informationcalculating section 128 transmits the calculated third densityunevenness correction information to the density correction processingsection 122.

Here, calculation methods for the first density unevenness correctioninformation, the second density unevenness correction information, andthe third density unevenness correction information are described belowin detail.

Next, the binarization processing section 130 carries out binarizationprocessing with respect to the image data which is directly transmittedfrom the image data transfer section 120 or the unevenness-correctedimage data which is transmitted from the density correction processingsection 122, and then generates a print control signal. Specifically, inorder to record the supplied image data on a recording medium, based onthe image data, the binarization processing section 130 determines ON/OFtiming of ejection (in other words, ejection pattern) for each ejectionportion of the recording head unit 50, and generates that timing as aprint control signal. The binarization processing section 130 transmitsthe generated print control signal to the head driver 116.

It should be noted that various kinds of processing methods may be usedfor the binarization processing section 130 to generate an ejectioncontrol signal from the image data. For example, a dithering method oran error diffusion method may be used.

Next, based on the ejection control signal (print data) provided fromthe print control section 112, the head driver 116 drives the actuatorof each ejection portion of the recording heads 50K, 50C, 50M, and 50Yof different colors. The head driver 116 may include a feedback controlsystem for keeping a head driving condition constant.

The image recording apparatus 10 is basically configured in theabove-mentioned manner.

Next, a method of creating the third density unevenness correctioninformation, which is used by the image recording apparatus 10, isdescribed. Here, the method of creating the third density unevennesscorrection information is performed in the same manner for any one ofthe recording heads 50K, 50C, 50M, and 50Y, and hence, the followingdescription is made concerning the recording head 50K as an example.

FIG. 7A is a side view illustrating a relation between each ejectionportion of the recording head and the landing position of an inkdroplet, and FIG. 7B is a top view associated with the side view of FIG.7A. It should be noted that, in FIGS. 7A and 7B as well as in thisembodiment as described hereinbelow, a plurality of ejection portionsarranged in line are defined as A1, A2, A3, . . . , and An in thearranged order from one end to the other end.

As illustrated in FIG. 7A and FIG. 7B, when an ink droplet ejected fromone ejection portion (in FIGS. 7A and 7B, ejection portion 60 numberedA5) is ejected in a different direction from ink droplets ejected fromother ejection portions, the position of impact point of that inkdroplet is displaced, that is, the landing position of the ink dropletis displaced. As a result, density unevenness occurs to the formedimage.

Further, as illustrated in FIG. 7A and FIG. 7B, when the ink amount ofan ink droplet ejected from one ejection portion (in FIGS. 7A and 7B,ejection portion 60 numbered A11) is smaller than a desired amount, animpact point formed by the ink droplet ejected from that ejectionportion 60 becomes smaller in size than the impact points of inkdroplets ejected from other ejection portions. Also when the size of theimpact point is different from the desired size, density unevennessoccurs to the formed image.

The above-mentioned third density unevenness correction information iscorrection information for correcting the ejection characteristics of anink droplet ejected from an ejection portion, such as the landingposition and the ink amount, which cause the above-mentioned densityunevenness.

By correcting the image data based on the third density unevennesscorrection information, even when an image is recorded using therecording head unit involving density unevenness, it is possible tocreate an image which seems to have no density unevenness on a recordingmedium.

FIG. 8 is a flow chart illustrating the steps of a process for creatingthe third density unevenness correction information. FIG. 9A is aschematic diagram illustrating an example of the first test pattern, andFIG. 9B is a partially enlarged view of FIG. 9A. Further, FIG. 10 is aschematic diagram illustrating an example of the second test pattern.Further, FIG. 11A is a graph illustrating an example of the firstdensity unevenness correction information for one recording element,FIG. 11B is a graph illustrating an example of the second densityunevenness correction information for one recording element, and FIG.11C is a graph illustrating an example of the third density unevennesscorrection information for one recording element. Each recording elementhas such density unevenness correction information as described above.

First, the recording head 50K draws the first test pattern on therecording medium P (Step S12).

Specifically, when a plurality of ejection portions arranged in lineare, as described above, defined as A1, A2, A3, . . . , and An in thearranged order from one end to the other end (see FIGS. 7A and 7B), theejection portions are divided into four groups of 4k-3, 4k-2, 4k-1, and4k (k=1, 2, 3, . . . ) based on the number of an ejection portion. Inkdroplets are ejected continuously from ejection portions having thenumbers expressed by 4k-3, and the lines are formed on the recordingmedium P by the respective ejection portions. Then, ink droplets areejected continuously from ejection portions having the numbers expressedby 4k-2, and the lines are formed on the recording medium P by therespective ejection portions. Then, similarly, with regard to ejectionportions having the numbers expressed by 4k-1, and ejection portionshaving the numbers expressed by 4k, the lines are formed on therecording medium P by the respective ejection portions.

By making a group with ejection portions spaced apart from each other atfixed intervals, it is possible to form lines without ejecting ink fromadjacent ejection portions. With this method, overlapping of lines canbe prevented.

Incidentally, in this embodiment, while the recording medium P isconveyed by the conveying portion 14 in the conveying direction, thatis, a direction perpendicular to the recording head 50K, ink dropletsare ejected from each ejection portion of the recording head 50K to formimpact points on the recording medium P.

In this manner, as illustrated in FIG. 9A and FIG. 9B, the first testpattern is formed on the recording medium P that consists of the linesformed by the respective ejection portions and grouped into four (G1,G2, G3, and G4) corresponding to the four groups of ejection portions.

Next, the first test pattern formed on the recording medium P is read bythe scanner 24 (Step S14).

Specifically, after the formation of the first test pattern, therecording medium P is further conveyed by the conveying portion 14, andpasses a position opposed to the scanner 24.

The scanner 24 reads the image formed on the recording medium P passingthrough the position opposed thereto, thereby reading the first testpattern. It should be noted that, at this time, the scanner 24 reads thefirst test pattern in a high resolution.

Further, the scanner 24 transmits the read image data to the firstdensity unevenness correction information calculating section 124 of thecontrol portion 22.

Next, the first density unevenness correction information calculatingsection 124 calculates the first density unevenness correctioninformation based on the first test pattern (Step S16).

First, based on image data obtained by reading the first test pattern inwhich the lines are formed by the respective ejection portions, thefirst density unevenness correction information calculating section 124calculates the landing position (ejection characteristic) of inkdroplets from each ejection portion.

Here, with regard to the landing position, as disclosed in JP2006-264069 A, for example, by detecting a density profile of each lineand calculating the center of each line based on the detection result,it is possible to calculate the landing position of ink droplets ejectedfrom each ejection portion.

Further, a method of calculating the center position is not limited inparticular. By detecting both edges of an ink droplet, the middle pointthereof may be set as the center, or a position having the highestdensity may be set as the center.

Further, with regard to the landing position, it is desirable that thecenters be calculated at a plurality of points in each line, and that anapproximate line be calculated by connecting the centers. Thecalculation of the approximate line by connecting a plurality of centersenables more accurate detection of the landing position of ink droplets.

Further, by extending the approximate line, it is possible to detectaccurately a relative positional relation among the groups. It should benoted that the relative positional relation can be obtained as follows.A reference ejection portion is set at the time of creating the firsttest pattern, and a line formed by the reference ejection portion isallowed to be formed in all of the four groups.

The first density unevenness correction information calculating section124 calculates the first density unevenness correction information basedon the calculated landing position information of each ejection portion.Here, the first density unevenness correction information is information(parameter or correction coefficient for each ejection portion) forcorrecting density unevenness based on the landing position informationof each ejection portion.

Here, a method of calculating the first density unevenness correctioninformation based on the calculated landing position information of eachejection portion is not limited in particular. The first densityunevenness correction information may be calculated based on the landingposition information by performing averaging processing so that thedensity of an area corresponding to an ejection portion comes close to areference density, as disclosed in JP 2006-264069 A. Alternatively, asdisclosed in JP 2006-347164 A, the first density unevenness correctioninformation may be calculated based on the landing position informationby performing numerical calculation processing among the ejectionportion in question and a plurality of ejection portions adjacentthereto.

Next, the recording head 50K draws the second test pattern on therecording medium P (Step S18).

Specifically, the recording head 50K ejects ink droplets from all theejection portions thereof to thereby record solid images (images havinga fixed density within a fixed area) having different densities. In thisembodiment, as illustrated in FIG. 10, solid images having densities of20%, 40%, 60%, 80%, and 100% are formed in image areas G5, G6, G7, G8,and G9, respectively.

Here, the print control section 112 corrects the second test patternusing the first density unevenness correction information calculated bythe first density unevenness correction information calculating section124, and converts the density-corrected second test pattern intoejection control signals. Then, based on the ejection control signals,the print control section 112 allows the drawing of the second testpattern on the recording medium P.

Specifically, the image data transfer section 120 transmits, to thedensity correction processing section 122, image data of the second testpattern (five solid images having different densities) transmitted fromthe system controller 104. The density correction processing section 122carries out the density unevenness correction processing with respect tothe second test pattern based on the first density unevenness correctioninformation. In other words, in order that density unevenness caused bya landing position error does not occur to the second test pattern to berecorded on the recording medium P, the density correction processingsection 122 carries out, with respect to the image data of the secondtest pattern, such density unevenness correction processing that takesinto account the landing position error of an ejection portion.

The density correction processing section 122 transmits the image dataof the density-corrected second test pattern to the binarizationprocessing section 130.

The binarization processing section 130 performs the binarizationprocessing with respect to the image data of the density-correctedsecond test pattern, and then generates an ejection control signal.Further, the generated ejection control signal is transmitted to thehead driver 116, and then, the recording head 50K records the image onthe recording medium P based on the ejection control signal, whereby thesecond test pattern is drawn.

Next, the scanner 24 reads the second test pattern formed on therecording medium P (Step S20).

Specifically, after the formation of the second test pattern, therecording medium P is further conveyed by the conveying portion 14, andpasses a position opposed to the scanner 24.

The scanner 24 reads the image formed on the recording medium P passingthrough the position opposed thereto, thereby reading the second testpattern. It should be noted that, at this time, the scanner 24 reads thesecond test pattern in a lower resolution than that in which the firsttest pattern is read.

Further, the scanner 24 transmits the read image data to the seconddensity unevenness correction information calculating section 126 of thecontrol portion 22.

Next, the second density unevenness correction information calculatingsection 126 calculates the second density unevenness correctioninformation based on the second test pattern (Step S22).

The second density unevenness correction information calculating section126 calculates density variation based on the image data obtained byreading the second test pattern in which a plurality of solid imageshaving different densities are formed.

Next, based on the calculated density variation, the ejected dropletamount (ejection characteristic) of each ejection portion is calculated.

Here, as described above, the second test pattern has been subjected tothe density unevenness correction based on the first density unevennesscorrection information, and hence, in a case where ink droplets having auniform droplet amount are ejected from the respective ejectionportions, an image with a fixed density, which has no density variation,is formed. Accordingly, density variation of a solid image can bedetected as fluctuation in the amount of droplets ejected from therespective ejection portions, and hence, based on the density variationand the landing position information calculated using the first testpattern, the amount of an ink droplet ejected from each ejection portioncan be calculated. Further, from the results of the above-mentionedcalculation, density unevenness caused by the fluctuation in amount(variation amount) of ink droplets ejected from the respective ejectionportions can be calculated.

Further, solid images having different image densities are created, and,based on a plurality of calculated values, the amount of an ink dropletejected from each ejection portion is calculated, and hence it ispossible to more accurately calculate the density unevenness caused bythe fluctuation in the amount of ink droplets. Further, it is alsopossible to calculate density unevenness caused by the fluctuation inthe amount of ink droplets for each density.

Next, the second density unevenness correction information calculatingsection 126 calculates the second density unevenness correctioninformation based on the calculated density variation caused by thefluctuation in the amount of ink droplets ejected from the respectiveejection portions. Here, the second density unevenness correctioninformation is information (parameter or correction coefficient for eachejection portion) for correcting the density unevenness caused by thefluctuation in the liquid amount of ink droplets ejected from therespective ejection portions.

For example, in a case where the amount of droplets ejected from anejection portion is smaller than the average, correction information formaking the setting so that ink droplets are ejected, with respect to aparticular image density, more frequently than those from the otherejection portions is calculated. In a case where the amount of dropletsejected from an ejection portion is larger than the average, correctioninformation for making the setting so that ink droplets are ejected,with respect to a particular image density, less frequently than thosefrom the other ejection portions is calculated. Further, such acorrection coefficient is calculated as below. In a case where thedensity of a particular area is low, the correction coefficient setshigher the ink ejection frequency of ejection portions corresponding tothe area, while in a case where the density of a particular area ishigh, the correction coefficient sets lower the ink ejection frequencyof ejection portions corresponding to the area.

Further, the present invention is not limited to correction which isperformed using the ejection frequency of one ejection portion. By usingadjacent ejection portions or the like, the correction coefficient maybe calculated so that an image which can be recognized, by the nakedeye, to have a desired density is formed or so that such a variationamount that cannot be recognized as unevenness by the naked eye can beattained.

Next, the third density unevenness correction information calculatingsection 128 calculates the third density unevenness correctioninformation (Step S24).

The third density unevenness correction information calculating section128 calculates the third density unevenness correction information basedon the first density unevenness correction information calculated by thefirst density unevenness correction information calculating section 124and the second density unevenness correction information calculated bythe second density unevenness correction information calculating section126. By calculating the third density unevenness correction informationbased on the first density unevenness correction information and thesecond density unevenness correction information, the third densityunevenness correction information serves as correction informationenabling to correct density unevenness caused by both the landingposition of an ink droplet ejected from an ejection portion and theamount of an ink droplet ejected from an ejection portion.

Specifically, using both a relation between input tone value on theabscissa and correction tone value on the ordinate, which is calculatedas the first density unevenness correction information with respect to arecording element and illustrated in FIG. 11A, and a relation betweeninput tone value on the abscissa and correction tone value on theordinate, which is calculated as the second density unevennesscorrection information with respect to a recording element andillustrated in FIG. 11B, such a relation between input tone value on theabscissa and correction tone value on the ordinate that is illustratedin FIG. 11C is calculated as the third density unevenness correctioninformation. The above-mentioned calculation is performed for everyrecording element, whereby correction information for all the recordingelements is calculated.

It should be noted that the calculation (composition) of third densityunevenness correction information Fc may be performed by combining firstdensity unevenness correction information Fa and second densityunevenness correction information Fb with the first density unevennesscorrection information Fa being a variable (that is, Fc=Fb(Fa)), or withthe second density unevenness correction information Fb being a variable(that is, Fc=Fa(Fb)).

In this manner, the image recording apparatus 10 calculates the thirddensity unevenness correction information.

Next, through description of a method of creating a print or a printedmaterial, which employs the image recording apparatus 10, the imagerecording method and the image recording apparatus according to thepresent invention are described in more detail.

FIG. 12 is a flow chart illustrating a process for processing image dataused for printing.

First, image data is input from the host computer 118 to the systemcontroller 104 via the communication interface 102.

After that, the image data is input from the system controller 104 tothe image data transfer section 120 of the print control section 112(Step S32).

The image data transfer section 120 transmits the input image data tothe density correction processing section 122.

The density correction processing section 122 uses the third densityunevenness correction information to carry out the density unevennesscorrection on the transmitted image data, and then createsdensity-corrected image data (Step S34).

The density correction processing section 122 transmits the createddensity-corrected image data to the binarization processing section 130.

The binarization processing section 130 carries out binarizationprocessing on the density-corrected image data, and then generates anejection control signal (Step S36).

After that, the binarization processing section 130 transmits theejection control signal to the head driver 116.

In this manner, the image data is processed, and transmitted to the headdriver 116.

Next, a recording operation performed by the image recording apparatus10 is described.

First, the recording medium P fed from the magazine 30 of the feedingportion 12 is subjected to the decurling processing by the heating drum32, and made flat. After that, the recording medium P is cut into apredetermined length by the cutter 34, and is fed to the conveyingportion 14.

The recording medium P fed to the conveying portion 14 is placed on thebelt 38 of the attraction belt conveying portion 36, and is conveyed bythe circulating belt 38.

The recording medium P conveyed by the attraction belt conveying portion36 passes through the position opposed to the heating fan 44 and isheated to a predetermined temperature, then passes through the positionopposed to the recording head unit 50. When the recording medium Ppasses through the position opposed to the recording head unit 50, inkdroplets are ejected from the respective recording heads in response tothe above-mentioned ejection control signals. Ink droplets ejected inorder of K, C, M, and Y land on the recording medium P, and an image isformed on the recording medium P.

It should be noted that, when the recording medium P passes through theposition opposed to the recording head unit 50, the recording medium Pis under suction by the attraction chamber 39, and hence a distancebetween the recording medium P and the recording head unit 50 is madeconstant. Further, while the recording medium P is conveyed, color inksare ejected from the respective recording heads 50K, 50C, 50M, and 50Y,whereby a colored image is formed on the recording medium P.

The recording medium P on which the image is formed by the recordinghead unit 50 is further conveyed by the belt 38, and passes through theposition opposed to the post-drying portion 53, at which position theimage area formed with ink is dried. The image is fixed by the pressureroller pair 54, and then, the recording medium P is discharged from thefirst discharging portion 58A.

In this manner, the image recording apparatus 10 draws (records) animage on the recording medium P, thereby creating a print or a printedmaterial.

As described above, according to the present invention, the firstdensity unevenness correction information for correcting densityunevenness caused by a landing position error and the second densityunevenness correction information for correcting density unevennesscaused by an ink droplet amount are calculated separately, and, based onthose two pieces of correction information, the third density unevennesscorrection information is calculated. Accordingly, it is possible tosuitably correct errors caused by both the landing position error andthe ink droplet amount, and an image having little or no densityunevenness can be recorded.

It should be noted that, in the description above, density unevenness tobe corrected by the first density unevenness correction information isassumed to be such density unevenness that is caused by a landingposition error, but the present invention is not limited thereto. Thefirst density unevenness includes high-frequency unevenness (densityunevenness having extreme variation) caused by various kinds of reasons(for example, ejection amount fluctuation). Further, density unevennessto be corrected by the second density unevenness correction informationis assumed to be such density unevenness that is caused by fluctuationin ink droplet amount, but the present invention is not limited thereto.The second density unevenness includes various kinds of low-frequencydensity unevenness (density unevenness having moderate variation), suchas concentration unevenness of ink ejected from each ejection portion.

Further, by calculating high-frequency density unevenness andlow-frequency density unevenness separately, the amount of image readingand the amount of image processing can be reduced, and also, densityunevenness can be suitably corrected.

Specifically, a landing position error needs to be calculated from theimage data acquired in a resolution exceeding the pixel recordingdensity, that is, the output resolution of the image recordingapparatus, at the time of outputting the first test pattern. Forexample, when the output resolution is 1,200 dpi, the resolution forimage data acquirement may be set to 1,200 dpi or more, for example, to2,400 dpi. With regard to the low-frequency density unevenness, anyresolution is applicable as long as unevenness visibly recognizable by ahuman can be read. Accordingly, in the case where low-frequency densityunevenness is detected from a solid image, the calculation is made basedon image data acquired by reading in a low resolution (for example, 100to 600 dpi), whereby the low-frequency density unevenness can becorrected. In consideration of the visual characteristics of a human, itis most desirable that the resolution at this time be set around 200 to300 dpi, which is a resolution high enough to equalize imperceptiblehigh-frequency unevenness.

In this manner, by also changing the resolution for reading an image inaccordance with each characteristic, it is possible to reduce the amountof image reading and the amount of image processing.

Here, as described above, it is desirable that the resolution forreading the first test pattern be set higher than the resolution of animage to be recorded by the recording heads. Specifically, inconsideration of the sampling definition, in order to obtain aresolution twice or more as high as the resolution of the recordedobject to be measured, it is desirable to set the reading resolutiontwice or more as high as the resolution (in this embodiment, forexample, 1,200 dpi) of an image recorded by the recording head unit (forexample, set to 2,400 dpi or more).

By reading in a resolution twice or more as high as the resolution ofthe recorded image, it is possible to calculate a landing position erroraccurately.

Further, the reading resolution required at this time may be setuniformly in the following manner only the resolution in a direction ofline of recording elements is set to be a high resolution (for example,2,400 dpi), and the resolution in a direction perpendicular to the lineof recording elements is set to be a low resolution (300 dpi). As aresult, the reading speed can be increased and the amount of data can bereduced.

Further, the first density unevenness correction information and thesecond density unevenness correction information do not have to becalculated at one time, but may be detected at separate timings. Forexample, only the second density unevenness correction information isupdated, and, with regarded to the first density unevenness correctioninformation, previous density unevenness correction information (alreadycalculated at the time of update) may be used.

Desirably, the first density unevenness correction information isupdated less frequently than the second density unevenness correctioninformation. As described above, with regard to the first densityunevenness correction information, an image needs to be read in a highresolution, and hence the amount of image reading and the amount ofimage processing are increased. However, a cause for high-frequencydensity unevenness to be corrected by the first density unevennesscorrection information, such as a landing position error, changes overtime by the influence of, for instance, time-dependent degradation ofthe surface of a recording head on which the openings of nozzles arelocated, and the change thereof is relatively moderate. Accordingly, thefirst density unevenness correction information does not changefrequently. On the other hand, a cause for low-frequency densityunevenness to be corrected by the second density unevenness correctioninformation, such as a drop amount of an ink droplet, depends ontemperature change as well, and hence it is necessary that the seconddensity unevenness correction information be updated at shorterintervals.

Accordingly, by updating only the second density unevenness correctioninformation, the amount of image processing can be reduced, and hencethe third density unevenness correction information can be calculated ina short period of time. Further, even if only the second densityunevenness correction information is updated without updating the firstdensity unevenness correction information, it is possible to correctdensity unevenness appropriately.

In this manner, by calculating the first density unevenness correctioninformation and the second density unevenness correction informationseparately, only necessary information can be updated, and hence itbecomes possible to calculate appropriate correction information with aless amount of processing.

Further, in the image recording apparatus 10, because a test pattern canbe created in a state in which high-frequency density unevenness hasbeen corrected, the image data of the second test pattern is correctedby the first density unevenness correction information, and, with theuse of the corrected image data of the second test pattern, the secondtest pattern is created. However, the present invention is not limitedthereto, and the second test pattern may be created without makingcorrection by the first density unevenness correction information.

When the second test pattern is created without making correction by thefirst density unevenness correction information, the amount of dataprocessing can be reduced at the time of creation of the second testpattern. It should be noted that, in this case, there may occur a casein which the amount of data processing increases when the third densityunevenness correction information is calculated.

Further, in the image recording apparatus 10, one scanner reads thefirst test pattern and the second test pattern recorded on a recordingmedium, but the present invention is not limited thereto. A scanner forreading the first test pattern and a scanner for reading the second testpattern may be provided separately.

As described above, by providing scanners separately, it is possible toprovide scanners dedicated to particular purposes. Specifically, as ascanner for reading the first test pattern, a scanner which reads animage in such a manner as to suitably calculate the position of animpact point (for example, scanner which is low in density gradation,but reads image in high resolution) can be used, while, as a scanner forreading the second test pattern, a scanner which reads an image in sucha manner as to suitably calculate the density variation (for example,scanner which is not high in resolution, but reads image with highdensity gradation) can be used.

With this configuration, density unevenness can be detected moreaccurately. In addition, switchover between the modes of the scannerbecomes unnecessary, and hence the operation becomes easier.

Here, in the case of providing separate scanners, it is desirable that,as the scanner for reading the first test pattern, a scanner capable ofreading an image in a higher resolution than the resolution of thescanner for reading the second test pattern be used.

Further, in the above-mentioned image recording apparatus 10, thescanner is provided inside the apparatus on the conveying path of therecording medium (that is, an in-line scanner is used), but the presentinvention is not limited thereto. The scanner may be provided at aposition apart from the conveying path of the recording medium, forexample, outside the enclosure of the image recording apparatus (thatis, an off-line scanner may be used). A recording medium on which animage is drawn in the image recording apparatus may be read by thescanner provided outside the enclosure of the image recording apparatus,and density unevenness may be detected with the same method as describedabove.

Further, in the above-mentioned image recording apparatus 10, a methodof directly reading a test pattern created by ejecting ink dropletstoward a recording medium inside the image recording apparatus isemployed, but the present invention is not limited thereto. The presentinvention is also applicable to a method of indirectly reading a testpattern.

Here, the indirect reading means that a test pattern created on arecording medium is temporarily transferred onto another recordingmedium for reading. In other words, the recording medium may also be anintermediate transfer member, and the present invention is applicable toa printer using a transfer method in which, after an image istemporarily drawn onto an intermediate transfer member, the image istransferred onto a final recording medium for obtaining an image.Further, in a case of directly reading a test pattern in a printer usingthe transfer method, an image on the intermediate transfer member is tobe read.

For example, the scanner for reading the first test pattern isconfigured by an off-line scanner, the scanner for reading the secondtest pattern is configured by an in-line scanner, and, as the scannerfor reading the first test pattern, one scanner that is common to aplurality of image recording apparatuses is provided. By doing so, thenumber of scanners which read an image in a high resolution can bereduced, which enables decreasing the cost on apparatus.

Incidentally, as described above, the first density unevennesscorrection information does not change abruptly, and hence may becalculated less frequently than the second density unevenness correctioninformation. Accordingly, even if it takes a long period of time for thecalculation due to a scanner provided as a separate member, there arisesalmost no problem in terms of driving apparatus.

Here, in this embodiment, as the first test pattern, the lines areformed in four groups, but the present invention is not limited thereto.The lines may be formed in two groups, in three groups, or in five ormore groups.

It should be noted that a landing position may be detected based on oneimpact point instead of forming lines as in the above-mentionedembodiment.

Further, as long as a state is such that adjacent impact points are notin contact with each other on a recording medium, that is, an impactpoint and its adjacent impact points are out of contact, impact pointsto be formed by all the ejection portions may be formed on one and thesame line in a direction perpendicular to the conveying direction of therecording medium.

For example, in a case where the size of an ink droplet to be ejectedcan be adjusted, that is, if the size of an impact point can beadjusted, an impact point may be made smaller by reducing an ink dropletto be ejected, whereby an impact point and its adjacent impact pointsare made out of contact.

In this manner, by preventing an impact point and its adjacent impactpoint from being brought into contact with each other, it is possible tocalculate both edges of each impact point in a reference directionaccurately.

Further, in this embodiment, image data is binarized by the binarizationprocessing section to generate an ejection control signal, but thepresent invention is not limited thereto. The image data may bedigitalized into N discrete values (N≧2) in accordance with the ejectioncapability of the recording heads. For example, in a case where therecording heads are capable of ejecting a large dot and a small dot, theimage data may be subjected to ternarization processing so as togenerate an ejection control signal having any one of three valuesindicating “large dot”, “small dot”, and “no ejection”.

Further, in this embodiment, the recording heads of the drawing portionare of a full-line head type, with their ejection portions beingarranged in one line, but the present invention is not limited to such aconfiguration comprising a single-line arrangement of ejection portions.As illustrated in FIG. 13, a recording head 50′K may be configured suchthat a plurality of lines of ejection portions are arranged in a zigzagby shifting the lines with a fixed pitch. In this manner, the ejectionportions 60 are arranged in a zigzag, and a line of impact points areformed by a plurality of lines of ejection portions, thereby enablingthe formation of an image having a higher resolution.

Further, in this embodiment, the recording head unit is configured inaccordance with the standard colors Y, M, C, and K (four colors), butthe color of ink, the number of colors, and combination thereof are notlimited to this embodiment. For example, light-colored ink ordark-colored ink may be added. More specifically, a configuration inwhich a recording head for ejecting light-colored ink, such as lightcyan or light magenta ink, is added is also applicable, and aconfiguration of a seven-color ink system in which inks of red (R),green (G), and blue (B) are added, for example, is also applicable.

Further, the recording head unit may be configured as a recording headfor ejecting only K-color (black) ink, that is, a single-color recordinghead unit, and the image drawing apparatus may be used for drawing asingle-colored image.

Hereinbefore, the image recording method and the image recordingapparatus according to the present invention have been described indetail, but the present invention is not limited to the above-mentionedembodiment, and various modifications and changes may be made withoutdeparting from the spirit and scope of the present invention.

For example, in the above-mentioned image recording apparatus,heat-curable ink is used, and the ink which has landed on a recordingmedium is fixed on the recording medium by the heat-pressing portion.However, the present invention is not limited thereto, and various typesof ink may be used. For example, in a case of using photo-curable ink, alight irradiation mechanism may be provided as a fixing portion.Activation energy-curable ink is ejected from a recording head, and animage is formed on the recording medium P with the photo-curable ink.After that, an activation light beam is irradiated to cure the image,whereby the image is fixed on the recording medium. Here, in a case ofusing UV curable ink as the photo-curable ink, various kinds ofultraviolet light sources, such as a metal halide lamp, a high-pressuremercury-vapor lamp, and a UVLED, may be used as the fixing portion.

Further, in this embodiment, the image recording apparatus is taken asan example, but the present invention is not limited thereto. Detaileddescription is given below with a specific example, but, to give oneexample, an image recording apparatus in which an image recorded on arecording medium P is heated and pressed, and the image is fixed on therecording medium P, may be used.

According to the present invention, two types of test patterns are usedto detect the density unevenness correction information for therespective characteristics, and, with the use of the third densityunevenness correction information calculated based on the both pieces ofdensity unevenness correction information detected, the image data issubjected to the density unevenness correction processing. As a result,the density unevenness can be corrected efficiently and accurately,enabling recording an image that has no or reduced image densityunevenness.

In addition, by detecting the correction information separately inaccordance with the characteristics, it is possible to reduce the amountof data processing and the cost on the apparatus.

What is claimed is:
 1. An image recording method of recording an imageon a recording medium while a recording head comprising a plurality ofrecording elements and the recording medium are moved relative to eachother, the image recording method comprising: a first recordingcharacteristic information acquiring step of causing each of therecording elements of the recording head to eject the ink droplet,forming a first test pattern on the recording medium, reading the formedfirst test pattern, and acquiring first recording characteristicinformation of the recording element based on a result of the reading; afirst density unevenness correction information calculating step ofobtaining first density unevenness correction information based on thefirst recording characteristic information; a second recordingcharacteristic information acquiring step of causing the each of therecording elements of the recording head to eject the ink droplet,forming a second test pattern different from the first test pattern onthe recording medium, reading the second test pattern, and acquiringsecond recording characteristic information of the recording elementbased on a result of the reading; a second density unevenness correctioninformation calculating step of obtaining second density unevennesscorrection information based on the second recording characteristicinformation; a third density unevenness correction informationcalculating step of obtaining third density unevenness correctioninformation based on the first density unevenness correction informationand the second density unevenness correction information; a densitycorrection processing step of correcting image data based on the thirddensity unevenness correction information to calculate densityunevenness-corrected image data; and an ejection control signalcalculating step of calculating an ejection pattern of the recordingelement based on the unevenness-corrected image data.
 2. The imagerecording method according to claim 1, wherein the second densityunevenness correction information calculating step comprises calculatingdensity unevenness having a lower frequency than a frequency of densityunevenness calculated in the first density unevenness correctioninformation calculating step.
 3. The image recording method according toclaim 1, wherein the first recording characteristic informationcomprises information at a position at which the ink droplet ejectedfrom the each of the recording elements lands on the recording medium.4. The image recording method according to claim 1, wherein the seconddensity unevenness correction information acquiring step comprisescreating the second test pattern based on the first density unevennesscorrection information.
 5. The image recording method according to claim1, wherein the second recording characteristic information acquiringstep comprises acquiring the second density unevenness correctioninformation at a higher frequency than a frequency at which the firstdensity unevenness correction information is acquired in the firstrecording characteristic information acquiring step.
 6. The imagerecording method according to claim 1, wherein: the first recordingcharacteristic information acquiring step comprises reading the firsttest pattern in a higher resolution than a resolution of a pixelrecording density for recording the first test pattern; and the secondrecording characteristic information acquiring step comprises readingthe second test pattern in a lower resolution than a resolution of thefirst recording characteristic information acquiring step.
 7. The imagerecording method according to claim 1, wherein the first recordingcharacteristic information acquiring step comprises reading the firsttest pattern in a resolution twice or more as high as a resolution ofimage data of the first test pattern.
 8. The image recording methodaccording to claim 1, wherein the first recording characteristicinformation and the second recording characteristic information eachcomprise density information for the each of the recording elements. 9.An image recording apparatus comprising: a recording head comprising aplurality of recording elements for ejecting an ink droplet toward arecording medium; movement means that causes the recording head and therecording medium to move relative to each other; recording operationcontrol means that records an image on the recording medium by causingthe recording head to eject the ink droplet toward the recording mediumwhile the recording head and the recording medium are moved relative toeach other; first test pattern reading means that reads a first testpattern formed on the recording medium by ejecting the ink droplet fromeach of the plurality of recording elements of the recording head; firstrecording characteristic information acquiring means that acquires firstrecording characteristic information of the each of the plurality ofrecording elements based on a result of the reading of the first testpattern; first density unevenness correction information calculatingmeans that obtains first density unevenness correction information basedon the first recording characteristic information; second test patternreading means that reads a second test pattern different from the firsttest pattern, which is formed on the recording medium by ejecting theink droplet from the each of the plurality of recording elements of therecording head; second recording characteristic information acquiringmeans that acquires second recording characteristic information of theeach of the plurality of recording elements based on a result of thereading of the second test pattern; second density unevenness correctioninformation calculating means that obtains second density unevennesscorrection information based on the second recording characteristicinformation; third density unevenness correction information calculatingmeans that obtains third density unevenness correction information basedon the first density unevenness correction information and the seconddensity unevenness correction information; density correction processingmeans that corrects image data based on the third density unevennesscorrection information to calculate density unevenness-corrected imagedata; and ejection pattern calculating means that calculates an ejectionpattern of the each of the plurality of recording elements based on theunevenness-corrected image data.
 10. The image recording apparatusaccording to claim 9, wherein: the first density unevenness correctioninformation calculating means calculates a position at which the inkdroplet ejected from the each of the plurality of recording elementslands on the recording medium, to thereby calculate the first densityunevenness correction information based on calculated landing positioninformation; and the second density unevenness correction informationcalculating means detects, based on density variation of the second testpattern, density unevenness caused by variation in amount of the inkdroplet ejected from the each of the plurality of recording elements, tothereby calculate the second density unevenness correction informationbased on the density unevenness caused by the variation in amount of theink droplet ejected from the each of the plurality of recordingelements.
 11. The image recording apparatus according to claim 9,wherein the first test pattern reading means and the second test patternreading means are configured as an identical means capable of switchingbetween resolutions.
 12. The image recording apparatus according toclaim 9, wherein the first test pattern reading means and the secondtest pattern reading means are absent from a conveying path of therecording medium conveyed by the movement means.
 13. The image recordingapparatus according to claim 9, wherein the first test pattern readingmeans and the second test pattern reading means are arranged on theconveying path of the recording medium conveyed by the movement means.14. The image recording apparatus according to claim 9, wherein: thefirst test pattern reading means is absent from the conveying path ofthe recording medium conveyed by the movement means; and the second testpattern reading means is arranged on the conveying path of the recordingmedium conveyed by the movement means.